Need boyfriend advice?

Alright, so I'll start from the very beginning. Freshmen year we met and we liked each other but I think we were just too immature to be in a relationship. We had continued to be friends and mostly just text each other until last April, junior year. He asked me to prom. I said yes. We had a great time. We went on a date and then became boyfriend/girlfriend. We had our first kiss on the second date. It's been going pretty well. Around other people I feel like it's kinda awkward, but when we are alone it's great. I think we are both pretty shy.

Our relationship is pretty sexual. Whenever we are alone together we fool around. Speaking in terms of bases, we are kinda in between 2nd and 3rd. I am not sure how I feel about going to 3rd quite yet. I know he wants me too, but he said he doesn't want me doing anything I'm not comfortable with. I think I want to do it, but I'm nervous and worried I'd mess up or something. Also, I don't want to always fool around whenever we are alone. How do I tell him that without hurting his feelings? Or how do I even bring that up?

Also, I run as my sport. I do cross country and track long distance. He jokes about that not being a real sport and it being easy and all that. It's really annoying because I work really hard and I really care about it. I know he's joking, but it still kinda hurts my feelings. What can I say to him?

My mom says he might be a little insecure, what do you think? And why would he be insecure and how can I make him feel more secure?

I'm just a little lost right now haha. I was trying to figure out what to do on my own and I couldn't and I also didn't rely have anyone I knew I could talk to.. So help me out please!

P.S. I do not want to break up. I think that this is something I can work out.